Maybe this could be a weapon for Hit and Run pyros?

+ -50% Airblast Cost (Meaning it only costs 10 ammo to use, maybe could be dumbed down to 15)
+ 50% Airblast Force
+ 50% Afterburn Damage
- 40% Damage
- 50% Airblast Speed (How many times you can airblast)

I dunno if this is deemed too OP or too UP, but I'm just saying this could be a Good flamethrower to use in Hit and Run situations (Light 'n Blow, possibly)

Seeing as how this here is a pesticide killer take a gander at this.

+Alt fire shoots fire.
+can ignite fire while gas is sprayed to create a semi-explosive attack. IE:Bigger burn radius.
Info:Attack sprays a gas substance.
-Does not airblast

Here’s my suggestion for stats, perfect for what the Pyro is unmatched in; hit and runs:

+ Afterburn deals 2% of target’s current max health as damage per half second
+ Airblast is constant stream as primary fire is but at twice rate of ammo cost
- -50% damage penalty

Here’s a graph to show the first mechanic, keeping in mind that all damage in TF2 is rounded up

Current Max Health of Ignited Enemy (h) ---- Afterburn Damage per Half Second for 10 seconds

50 < h ≤ 100 ------------------------------------------- 2
100 < h ≤ 150 ------------------------------------------ 3
150 < h ≤ 200 ------------------------------------------ 4
200 < h ≤ 250 ------------------------------------------ 5
250 < h ≤ 300 ------------------------------------------ 6

-25% damage
+50% afterburn length
Green Flame (+1% fancy)
No airblast

This does seem to be a chemical thrower rather than a flame thrower. Intriguing.

+ On hit: target is poisoned for 6 seconds
+ On hit: target is gassed for 6 seconds
+ Primary Fire: 100% Slower ammo consumption

- Primary fire does not light targets on fire
- No Afterburn
- -100% Damage